In general, semiconductor materials may be processed in semiconductor technology on or in a substrate (also referred to as a wafer or a carrier), e.g. to fabricate integrated circuits (also referred as to chips). During processing the semiconductor materials certain process steps may be applied, such as thinning the substrate or forming one or more layers over the substrate.
Thinning the substrate may include removing material from a backside of the substrate. The remaining thickness of the thinned substrate is a critical parameter which influences among other parameters the robustness against electrical short circuits, e.g. due to the resulting distance between emitter and field stop zone in insulated-gate bipolar transistors (IGBT). Therefore, a precise adjustment for the thinning is a key parameter for controlling the performance and reliability of the readily processed chips.
In further processing of the semiconductor material, certain impurity atoms may diffuse out of the substrate, e.g. nitrogen or oxygen. Since the presence and concentration of the impurity atoms influence the electrical properties of certain active regions of the substrate, e.g. the drift zone of an IGBT, this may impair the performance of the readily processed chips. For example, reduced oxygen may lead to thermal donors and reduced nitrogen may reduce the doping of the drift zone or the doping of the field stop zone.
Conventionally, for thinning the substrate (thinning process) grinding in combination with etching is used, or, if more accurate control of wafer thickness is needed, electrochemical etching is used. The electrochemical etching is self-adjusting with respect to the border of a space charge region. Such conventional processes are very sensitive in their preciseness. For example, the doping level influences the extent of the space charge region such that the self-adjusting cannot be sufficiently precise. Therefore, conventional methods require extreme effort to realize a precise self-adjustment effect.